Many clay deposits often need to be stabilized before they can carry any additional load such as is applied during construction activities. This is specially true for the so-called quick clays which frequently are found, for example, in northern Soviet Union, Scandinavia, Canada, upper New York State, and New Zealand. Clays were originally deposited in marine and brackish water in a short period after the last glaciation, and later during the continental (isostatic) uplift were raised above sea level. However, only certain of these clay deposits were subsequently changed into sensitive quick clays. Two processes are mainly responsible for such a change. The original pore water salt content of the clay may have been leached by percolating ground water, or organic matter from logs or marshes which will act as dispersing agents may have been introduced into the clay. The first process has been most important in clays found in Norway, while quick clays containing high organic content formed by the second process are frequently found in Sweden and Canada.
The quick clays will in the undisturbed state exhibit a certain limited strength, but will upon remoulding completely liquefy. This same phenomena has caused several quick clay slides in the lowlands of eastern and middle Norway, often with catastrophic consequences. Heretofore, several chemical stabilization schemes have been tried for such clays. Among them were aluminum chloride (AlCl.sub.3) and potassium chloride (KCl). The quick clays have been stabilized in two ways. The clay can be mixed and remoulded with the chemicals, or the chemicals can be allowed to diffuse into the undisturbed quick clay. The disadvantage of the salt diffusion method is the long time it takes to reach the required penetration. The diffusion method has been applied only once, so far as is known, in full scale in the field, when salt wells containing KCl were installed two years prior to a major highway construction.
Heretofore, a method for deep stabilization with unslacked lime (CaO) was developed. Lime is an old stabilizing agent that has been used occasionally. In China it was used centuries ago as a construction material. In the U.S.A. in the 1940's and Europe in the 1950's lime was used as a surface stabilizing agent. The deep stabilization method involves mixing and molding the lime with the clay to form a series of piles which extend down into the clay. These piles provide lateral stabilization to the clay deposit.
Both the lime and potassium chloride methods have some disadvantages. KCl will stabilize the undisturbed circumjacent clay, but not the disturbed clay. Furthermore, CaO makes an unhomogenous stabilization. Pockets of lime cause brittle cylinders with small sideways shear strength. In addition, CaO is not useful on clays with high water content. While hydroxy-aluminum as Al(OH).sub.2.5 Cl.sub.0.5 has not been used as a clay stabilizing agent in foundation engineering before it has been applied as a cementing agent in preparing desired clay microstructures for laboratory studies. Hydroxy-aluminum solution containing KCl has also been used in wells to treat water sensitive clay containing formations and to provide sand stabilization. Relatively dilute solutions and overflushes are commonly used in the field. These methods are disclosed in U.S. Pat. No. 3,603,399 issued Sept. 7, 1971 and No. 3,827,495 issued Aug. 6, 1974 both to Marion G. Reed as assignor to Chevron Research Company.
The above-cited Related Applications provide for stabilizing clay soil by admixing an effective amount of hydroxy-aluminum and in some cases additional chemicals such as potassium chloride with the clay. While potassium chloride is preferred, other chemicals useful in place of potassium chloride include potassium nitrate, potassium sulfate, ammonium chloride, ammonium nitrate and ammonium sulfate. The admixture is preferably done in a manner so that the stabilized clay forms a series of piles which extend into the clay deposit at spaced apart location to provide stability for the entire clay containing deposit. The desired size, location and number of the piles are determined. An effective amount of hydroxy-aluminum is admixed with the clay in place in each location in the deposit to react with the clay and thereby form the desired piles.
It has been found that the addition of other material can improve the method described above.